Scratchcards which claim to offer extravagant prizes leave most "winners" out of pocket by encouraging them to call premium rate telephone lines, the Office of Fair Trading (OFT) warned today.

The scratchcards, usually distributed in newspapers and magazines, give the recipient the impression they have won a top prize, gift or award.

To find out what they have won the recipient is encouraged to call a premium rate phone number - a call which often costs more than £10 in total.

Almost all of the "prizes" have strict limitations attached to their use, the OFT found. All of the scratchcards surveyed by the OFT were so-called "winners".

The holiday prizes - which included a Caribbean cruise and trips to the Canaries, Barcelona and France - were generally for one person only and most had to be taken with as little as seven days' notice.

There were also strict deadlines for completion of forms and some required an additional processing fee.

Details of terms and conditions on the cards were lengthy, small and difficult to read, it found.

The OFT said the discount vouchers offered as prizes were typically time limited and could only be redeemed through a specified agent.

John Vickers, OFT chairman, said: "These promotions tell everyone that they are winners. In fact most who respond end up as losers."

A spokesman added: "By and large the majority of people who respond are disappointed. A lot of these scratchcards are not necessarily providing what they claim to. There may be strings attached.

"Our best advice is to read the small print. Stop and think before you phone up."

George Kidd, director of premium rate services' regulator ICSTIS, said: "Under our code of practice call costs must be clearly given, as must details of the number of prizes available and any terms and conditions, including additional costs, associated with claiming those prizes.

"We will continue to take swift action against any company that breaks these rules."